Considering tackling an off-grid install. Power consumption is a concern. I tried unsuccessfully to convince the client to install the boiler in the basement and do a normal upfeed gravity system which would have been hard enough considering I've never done gravity feed (who has?). Boiler must be outside so a pump is needed and can be used to also supply basement/DHW. My question is: it seems like a waste to have hot water piped to the basement and not take advantage of a gravity feed setup. I'd like to keep it closed/pressurized but am trying to wrap my head around this ancient technology. Could I just use a hydraulic sep and run the upper floors off there? Or will I need an Xchanger to properly separate flows? Has anyone installed a gravity system in the last 100 years? Maybe on an Amish farm?
hybrid forced/gravity circulation
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RobC
Minister of Fire
I can't answer you gravity system question but, there is a book being put together that will address some new ideas and issues. The author(s) asked on this forum for some ideas to be included and one was how to reduce power consumption. I don't know how that has progressed, or if that topic will be included. Maybe we will get an update.
One thing that may be a problem for long term gravity system would be the recommended use of a loading valve. For that to operate you'd most likely need a pump.
There are an assortment of 12V pumps that you could use on the zones if necessary. There are many with engineering backgrounds that visit this forum but things are a bit slow during summer. This is a good place to look for answers. I think with some with patience you could get some good answers. Interesting topic.
If a gassifier is going in read up on wood and moisture content. You need to have dry wood for gassers. Good time to take care of that.
More info is always helpful, where do live, stove etc......
Rob
One thing that may be a problem for long term gravity system would be the recommended use of a loading valve. For that to operate you'd most likely need a pump.
There are an assortment of 12V pumps that you could use on the zones if necessary. There are many with engineering backgrounds that visit this forum but things are a bit slow during summer. This is a good place to look for answers. I think with some with patience you could get some good answers. Interesting topic.
If a gassifier is going in read up on wood and moisture content. You need to have dry wood for gassers. Good time to take care of that.
More info is always helpful, where do live, stove etc......
Rob
Nothing magic about gravity circulating systems. The key is to make certain the path of the hot supply water only travels up or horizontal (more up is better) and the path of the cooler return water is only down or horizontal (more down is better).
The hard part is cost because in order to get the resistance to flow as low as possible, larger than ordinary piping is required and that adds up to much higher costs than the typical pumped system.
I lived off-grid for years. PV setup and all. For a mortgage-free person it always came down to the scary up front costs of hardware. If the cost can be rolled into a mortgage then it might soften the blow.
Laing makes high quality circulators that run on low voltage DC. I've seen them referenced in discussions here from off-grid folks. No personal experience.
If this place will have inverter 120VAC available one of the new high-efficiency ECM circulators like the Grundfos Alpha might be a smaller electrical load than DC. That would take some electrical engineering I don't have to know for sure. Best price I know for the Alpha is here at Patriot Supply: http://www.patriot-supply.com/products/showitem.cfm/200930
I think for any new construction, off-grid or not, using larger distribution piping and smaller more efficient circulators is a long term saving. But from the price I have seen recently at lowes-depot for large pipe sizes, getting pipe large enough to gravity flow through a whole house might be more money than circulator driven systems done right.
The hard part is cost because in order to get the resistance to flow as low as possible, larger than ordinary piping is required and that adds up to much higher costs than the typical pumped system.
I lived off-grid for years. PV setup and all. For a mortgage-free person it always came down to the scary up front costs of hardware. If the cost can be rolled into a mortgage then it might soften the blow.
Laing makes high quality circulators that run on low voltage DC. I've seen them referenced in discussions here from off-grid folks. No personal experience.
If this place will have inverter 120VAC available one of the new high-efficiency ECM circulators like the Grundfos Alpha might be a smaller electrical load than DC. That would take some electrical engineering I don't have to know for sure. Best price I know for the Alpha is here at Patriot Supply: http://www.patriot-supply.com/products/showitem.cfm/200930
I think for any new construction, off-grid or not, using larger distribution piping and smaller more efficient circulators is a long term saving. But from the price I have seen recently at lowes-depot for large pipe sizes, getting pipe large enough to gravity flow through a whole house might be more money than circulator driven systems done right.
ewdudley
Minister of Fire
As Dave suggests, a constant-pressure ECM pump working together with gravity would require smaller tubing and very little power.
There are a few Siegenthaler articles out there concerning various aspects of the problem. Here's one where he presents the advantages of home-run circuits with fairly small tubing and low-wattage pumping requirements:
http://www.pmengineer.com/Articles/Cover_Story/BNP_GUID_9-5-2006_A_10000000000000187323
Cheers --ewd
There are a few Siegenthaler articles out there concerning various aspects of the problem. Here's one where he presents the advantages of home-run circuits with fairly small tubing and low-wattage pumping requirements:
http://www.pmengineer.com/Articles/Cover_Story/BNP_GUID_9-5-2006_A_10000000000000187323
Cheers --ewd
Thanks guys. The Siegenthaler articles are great. I've checked out the Wilo ECO pumps and the Liangs. Tough choice since 24VDC and 120AC is available. I think either would work well. This project got me thinking about saving power in general which I think will only become more important to everyone as things go along. He knows the larger pipes and rads will cost more. The boiler is not a gasser since they all need fans. Rads with TRV's will do the emitting/zoning. I think I might try the hydro sep based on the dyed water pics on the Caleffi site. ground & upper floor to run by gravity off the sep and the forced boiler loop to heat the basement & DHW. The siding and exterior insulation are getting replaced and gives a guy a chance to do a top-notch install. I dug up a different gravity set-up that had an "express riser" that runs straight up above the height of the highest rads, then feeds straight back down through all the rads, slick as hell. I guess if the sep is hot and the rads above it are cool and the lines are big, nature will do the rest. I hope anyway. Maybe a flapper check or 2 just to make sure its going the right direction all the time. I'll have to sharpen the pencil and finger out pipe sizes and all.
ewdudley - I see what you're saying, DON'T separate flows and try to have a gravity-assisted pumped system. I'm leery of trying that in case I wind up with funky short-circuiting issues. I've read articles where guys have lots of problems adding a pump to a former gravity system. The pump has little backpressure and sees all these low pressure change areas and behaves unpredictably or backfeeds down the same pipe, etc. Is what they say anyway.
ewdudley - I see what you're saying, DON'T separate flows and try to have a gravity-assisted pumped system. I'm leery of trying that in case I wind up with funky short-circuiting issues. I've read articles where guys have lots of problems adding a pump to a former gravity system. The pump has little backpressure and sees all these low pressure change areas and behaves unpredictably or backfeeds down the same pipe, etc. Is what they say anyway.
ewdudley
Minister of Fire
flameretardant said:
Check out the Varmebaronen natural draft units. I think SmokelessHeat has them.
--ewd
ewdudley
Minister of Fire
flameretardant said:
Yeah my current residence is a converted gravity system and I get some amusing things going on.
But if I understand the Siegenthaler stuff I believe he's saying go with a buffer-tank/hydraulic separator that is supplied from the boiler, and then feed all your zones in parallel with home-run circuits fed by a single constant-pressure ECM pump that will augment gravity flow to small extent necessary.
--ewd
That Sieganthaler system is interesting. But the 40 watts consumption was only on the house side. With the 2 other circs, there would be more usage. Its rare a hack like me could spot an error in an engineer's work, but if Siegenthaler simply flipped the buffer tank on top of the boiler, he could eliminate a circ. Put the DHW tank on top of that and theres another one gone. Sell the whole shebam as a boiler/buffer/DHW solution that removes dirt and air and uses -zero- electricity and you've got the latest in new old technology. The upsized pipe used might be short enough to compete with circs on an up-front basis. Add an ECM circ to supply the house. beautiful. Now I just gotta convince the guy to put the damn thing in his basement!
RobC
Minister of Fire
Here is a gravity radiant wall system that an off-gridder friend built. He bought ThermaFin, solar collector absorber strips and mounted them with a generously sized, sloped upper and lower header.
He used greenhouse window operators to move ball valves for "thermostats"
Being frugal, he used Vodka as the antifreeze heat transfer fluid in his solar array. instead of glycol.
Larry lives in Northern California and like to talk solar and off grid living. i can put you in touch with him to share data.
hr
He used greenhouse window operators to move ball valves for "thermostats"
Being frugal, he used Vodka as the antifreeze heat transfer fluid in his solar array. instead of glycol.
Larry lives in Northern California and like to talk solar and off grid living. i can put you in touch with him to share data.
hr
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That would be great. I'm having a devil of a time finding formulae for gravity systems. I found a few @ engineeringtoolbox.com. I am trying to figure out what pipe size i need but manufacturers don't list head loss numbers for thier piping below what is considered a minimum pumped flow rate. In the CI radiator thread, there's a pic of a cat sleeping on a gravity-fed rad - the pipe for that one rad must be 1 1/4! I'd like to use pex for the smoothness, cost and corrosion resistance, pex supply has it up to 4". I'd like to move 100 000btu. Lots of homework to do yet...
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